A spiralling oversupply of shared bikes in China is leading to huge piles of broken and unused bicycles in cities across the country.

Over the past year, about 30 companies have madly pumped out millions of new bicycles from factories, distributing them in major centres in a battle for market share.

The two biggest companies, Ofo and Mobike, claim to collectively have 20 million users registered with their services.

The bicycle boom has revived cycling in a country that was once affectionately referred to as the bicycle kingdom, prior to three decades of high-speed economic growth that flooded the streets with cars.

But now there is growing concern about a bubble, as big investors rush to pour money into bike sharing.

The key appeal of the shared bikes — that they do not need to be returned to a dock — is proving problematic in busy spots, where bikes are piling up and blocking pedestrians.

PHOTO Broken and discarded shared bikes pile up in a Beijing backstreet.